The present invention relates to a two-barrel carburetor for use with automobile engines, and, more particularly, an improvement of a kick-up device for the secondary throttle valve of a diaphragm-type two barrel carburetor wherein the secondary throttle valve is opened by a diaphragm means actuated by venturi vacuum of the secondary venturi portion included in the secondary bore of the carburetor.
Modern automobile engines generally employ two-barrel carburetors having primary and secondary bores including primary and secondary venturi portions respectively, primary and secondary main fuel nozzles provided in the primary and secondary venturi portions respectively, primary and secondary throttle valves provided in the primary and secondary bores respectively, etc., wherein the primary throttle valve is directly operated to be opened or closed by the accelerator pedal via an accelerator linkage mechanism, while the secondary throttle valve is operated to be opened or closed by, in most cases, a diaphragm means, actuated by venturi vacuum of the primary venturi portion in a manner such that, when the air flow through the primary bore or venturi portion increases beyond a predetermined value, the secondary throttle valve is opened to put the secondary system into operation. Carburetors of this type are known as diaphragm-type two barrel carburetors.
Conventionally, a diaphragm-type two barrel carburetor incorporates a kick-up device for the secondary throttle valve which forcibly opens the second throttle valve by a very small opening such as 1.degree. when the primary throttle valve is opened beyond a predetermined opening in order to prevent delaying of opening of the secondary throttle valve due to sticking of the secondary throttle valve to the wall of the secondary bore or frictional engagement which may occur therebetween, such delay otherwise being liable to occur, when the secondary throttle valve must be opened starting from its fully closed position by the diaphragm means.
Heretofore, these carburetors have been generally adjusted to produce fuel-air mixture of an economical, or lean, air/fuel ratio in medium load operation while producing a richer fuel-air mixture in high load operation by employing a power fuel system. However, in recent years, carburetors are often adjusted to produce a slightly richer fuel-air mixture than ever in order to compensate for a deterioration of combustibility of fuel-air mixture due to exhaust gas recirculation as well as in order to reduce generation of NOx. In most carburetors for automobile engines, the power fuel supply system is adjusted to produce fuel-air mixture of an optimum air/fuel ratio in 3/4 load operation. Therefore, if the air/fuel ratio in low to medium load operation is adjusted to be slightly richer than the most economical air/fuel ratio, the carburetor produces an over-rich fuel-air mixture in full load low-speed operation, which causes various drawbacks, such as power reduction, poor fuel economy, carbon contamination of spark plugs, etc..